Compositions: ceramic – Ceramic compositions – Aluminum compound containing
Reexamination Certificate
2000-01-27
2001-10-23
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Aluminum compound containing
C501S127000, C264S674000, C313S636000
Reexamination Certificate
active
06306788
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a translucent alumina sintered body having high linear transmittance and a method for producing the same.
DESCRIPTION OF THE RELATED ART
In conventional high purity alumina powders, fine particles coagulate each other or coarse particles are present heterogeneously, therefore, sintering speed is non-uniform and coarse pores remain in large number. A coarse pore having a size of several &mgr;m or more is difficult to be removed only by optimization of a sintering agent, and also there is a limitation on linear transmittance of the final sintered body.
For obtaining high translucency, there is known a technique in which, for example, ruthenium oxide, lanthanum oxide and the like are added in addition to magnesium oxide, and refractive index of spinel phase on grain boundary is allowed to approximate that of alumina to improve translucency (Japanese Patent Application Publication (JP-B) No. 49-15447). However, this method has been problems that uniform dispersion of trace components heavier than aluminum oxide is difficult, consequently, microstructure of sintered body easily becomes non-uniform, and whole light transmittance lowers due to absorption of lights by these trance components.
Also, there is known a technique in which calcium oxide having an effect for promoting grain growth of alumina is added in addition to magnesium oxide, and sintered body system is enlarged to increase translucency. However, there has been a problem that mechanical strength decreases by enlargement of the system (JP-B No. 54-148008).
SUMMARY OF THE INVENTION
The present inventors have intensively studied to solve the above-described problems, and found that a translucent alumina sintered body having higher translucency than that of conventional one while maintaining the same structure of sintered body as that of the conventional one can be obtained by adding alumina which has a BET specific surface area of 5 to 200 m
2
/g and a sintering agent to an &agr;-alumina powder comprising a polyhedral primary particle having substantially no fractured surface, forming the mixture and sintering the formed product under the condition of hydrogen atmosphere from atmospheric pressure to vacuum at a temperature from 1600 to 1900° C.
That is, the present invention provides a method for producing a translucent alumina sintered body comprising the steps of:
forming a raw material powder, and
sintering the formed product under the condition of hydrogen atmosphere from atmospheric pressure to vacuum at a temperature from 1600 to 1900° C.,
wherein the raw material powder is a mixed powder comprising
an &agr;-alumina powder (1) which comprises a polyhedral primary particle having substantially no fractured surface, has a BET specific surface area of 1 to 7 m
2
/g, and has a purity of 99.99% or more,
an alumina powder (2) having a BET specific surface area of 5 to 200 m
2
/g in an amount of 10% by weight or less based on said &agr;-alumina powder, and
a sintering agent, and satisfies the following formula:
(BET specific surface area of alumina powder (2))−(BET specific surface area of &agr;-alumina powder (1))>2 m
2
/g.
Also, the present invention provides a translucent alumina sintered body having an average grain size of 20 to 50 &mgr;m, and having linear transmittance of a light which has a wavelength of 600 nm passing through a plate having a thickness of 0.85 mm is from 50 to 70%.
REFERENCES:
patent: 4799601 (1989-01-01), Shimai et al.
patent: 0 567 095 A1 (1993-10-01), None
patent: 49-15447 (1974-04-01), None
patent: 54-148008 (1979-11-01), None
patent: 6-191833 (1994-07-01), None
patent: 6-191836 (1994-07-01), None
Uchida Yoshio
Watanabe Hisashi
Koslow C. Melissa
Sughrue Mion Zinn Macpeak & Seas, PLLC
Sumitomo Chemical Company Limited
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